1. Field of the Invention
The present invention pertains to telecommunications, and particularly to the switching from dedicated to common channels in a wireless telecommunications system.
2. Related Art and other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (xe2x80x9ccellularxe2x80x9d telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term xe2x80x9csoft handover.xe2x80x9d In contrast to hard handover, soft handover is a xe2x80x9cmake-before-breakxe2x80x9d switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks)
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the xe2x80x9cIuxe2x80x9d interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the xe2x80x9cIubxe2x80x9d interface. The interface between the user equipment unit (UE) and the base stations is known as the xe2x80x9cair interfacexe2x80x9d or the xe2x80x9cradio interfacexe2x80x9d or the xe2x80x9cUu interfacexe2x80x9d. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC (see, in this regard, U.S. patent application Ser. No. 09/035,821 filed Mar. 6, 1998, entitled xe2x80x9cTelecommunications Inter-Exchange Measurement Transferxe2x80x9d; and U.S. patent application Ser. No. 09/035,788 filed Mar. 6, 1998, entitled xe2x80x9cTelecommunications Inter-Exchange Congestion Controlxe2x80x9d, both of which are incorporated herein by reference). The interface between a SRNC and a DRNC is termed the xe2x80x9cIurxe2x80x9d interface.
The Universal Mobile Telecommunications (UMTS) has both common transport channels and dedicated transport channels. The common transport channels are the random access channel (RACH), the forward access channel (FACH), the common packet channel (CPCH), and the downlink shared channel (DSCH). The dedicated transport channels include the dedicated channel (DCH). These transport channels are described, e.g., in one or more of the following three specifications:
(1) 3GPP TS 25.211, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (FDD)xe2x80x9d.
(2) 3GPP TS 25.221, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (TDD)xe2x80x9d.
(3) 3GPP TS 25.331, v.3.2.0 xe2x80x9cRRC Protocol Specificationxe2x80x9d.
In the foregoing, xe2x80x9c3GPPxe2x80x9d refers to a project known as the Third Generation Partnership Project (3GPP), which has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.
From a resource management point of view, the downlink shared channel (DSCH) is managed by the network (UTRAN) in a similar way as the dedicated channel (DCH). Thus, from the resource management point of view, the downlink shared channel (DSCH) is essentially a dedicated resource. Accordingly, as used herein, a xe2x80x9ccommon channelxe2x80x9d is any one of the common transport channels excluding the downlink shared channel (DSCH), and a xe2x80x9cdedicated channelxe2x80x9d herein means dedicated transport channels and the downlink shared channel (DSCH).
On various occasions, it may be necessary or desirable to switch from a common channel to a dedicated, or conversely from a dedicated channel to a common channel, using what has been termed xe2x80x9cchannel switchingxe2x80x9d. Various techniques for channel switching are described in the following United States Patent Applications, all of which are incorporated herein by reference: U.S. patent application Ser. No. 09/429,497 (attorney reference 2380-150), filed Oct. 28, 1999, entitled xe2x80x9cChannel-Type Switching To A Common Channel Based On Common Channel Loadxe2x80x9d; U.S. patent application Ser. No. 09/457,141 (attorney reference 2380-165), filed Dec. 8, 1999, entitled xe2x80x9cChannel-Type Switching Controlxe2x80x9d; U.S. patent application Ser. No. 09/537,689, filed Mar. 29, 2000, entitled xe2x80x9cChannel-Type Switching Based On Cell Loadxe2x80x9d.
When switching a connection from common channels to dedicated channels in UMTS, the network (UTRAN) selects the radio resources. Furthermore, in order to request that the user equipment unit (UE) switch to the selected dedicated channels, the network (UTRAN) sends information describing the selected resources to the user equipment unit (UE) using certain signaling messages in a physical channel reconfiguration procedure, as described, e.g., in 3GPP TS 25.331, v.3.2.0 xe2x80x9cRRC Protocol Specificationxe2x80x9d. In the context of this particular switch, the radio resources are the physical channel and transport channel resources for the dedicated transport channels (DCH) and/or downlink shared channel (DSCH) to be employed. The physical channel resources are those such as uplink DPCH, downlink DPCH, and/or downlink physical DSCH. For a definition of these channels and more detailed information, see, e.g., 3GPP TS 25.211, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (FDD)xe2x80x9d or 3GPP TS 25.221, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (TDD)xe2x80x9d.
When switching from dedicated channels to common channels in UMTS, on the other hand, there are two different or alternative ways of assigning radio resources to be used by a user equipment unit (UE). In the context of this type of channel switching, the radio resources are the physical channel and transport channel resources for the common transport channels RACH, FACH, and/or CPCH (but not including the downlink shared channel (DSCH)). The physical channel resources are those such as the primary CPICH, secondary CCPCH, and/or physical RACH. For a definition of these channels and more detailed information, again see, e.g., 3GPP TS 25.211, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (FDD)xe2x80x9d or 3GPP TS 25.221, v.3.2.0 xe2x80x9cPhysical Channels and Mapping of Transport Channels Onto Physical Channels (TDD)xe2x80x9d.
A first of the alternate ways of assigning radio resources when switching from dedicated channels to common channels in UMTS is to let the user equipment unit (UE) select the radio resources. When the user equipment unit (UE) is to switch to the common channels, the network sends information that the user equipment unit (UE) shall switch to common channel resources via signaling messages in accordance with a physical channel reconfiguration procedure (described, e.g., in 3GPP TS 25.331, v.3.2.0 xe2x80x9cRRC Protocol Specificationxe2x80x9d). The user equipment unit (UE) then, as a result of receipt of the signaling message, enters a state know as the Cell_FACH state, in which the user equipment unit (UE) detects and reads the broadcast channel in the cell to find the radio resources to be utilized for the common channel (e.g., as in an RCC Connection Re-establishmentxe2x80x9d procedure. The UMTS provides certain rules which govern the selection of radio resources for this alternative, as described in 3GPP TS 25.331, v.3.2.0 xe2x80x9cRRC Protocol Specificationxe2x80x9d.
A second of the alternate ways of assigning radio resources when switching from dedicated channels to common channels in UMTS is for the network (UTRAN) to select the radio resources. When the user equipment unit (UE) is to switch to the common channels, the network sends information describing the network-selected resources to the user equipment unit (UE) via signaling messages in accordance with a physical channel reconfiguration procedure (described, e.g., in 3GPP TS 25.331, v.3.2.0 xe2x80x9cRRC Protocol Specificationxe2x80x9d).
Moreover, regardless of whether the first or second alternatives described above are implemented, when switching from dedicated to common channels in UMTS the user equipment unit (UE) is also assigned a temporary identifier known as C-RNTI. This temporary identifier, the C-RNTI, is valid in the cell where the user equipment unit (UE) utilizes resources, and is used to distinguish between different user equipment units (UEs) in that cell.
The current 3GPP proposals envision switching from common channels to dedicated channels regardless of whether the user equipment unit (UE) is in a cell controlled by the serving RNC (SRNC) or the drift RNC (DRNC). However, for switching from dedicated channels to common channels, the second alternative way summarized above (i.e., the alternative in which the network assigns the radio resources to be used) can be used, but only if the user equipment unit (UE) is in a cell under the control of the serving RNC (SRNC). In other words, if the user equipment unit (UE) is in a cell under the control of the drift RNC (DRNC) rather than the serving RNC (SRNC), it is not possible for the network to assign the radio resources to be used when switching from dedicated channels to common channels.
Thus, in the current 3GPP proposals there are restrictions upon switching from dedicated channels to common channels. These restrictions include the fact that the serving RNC (SRNC) cannot assign the necessary temporary identifier C-RNTI or the necessary radio resources to be used when requesting that the user equipment unit (UE) switch to common channels if the user equipment unit (UE) is in a cell under control of the drift RNC (DRNC) rather than the serving RNC (SRNC). The network not being able to assign a temporary identifier C-RNTI for the user equipment unit (UE) leads to longer signaling sequences between the user equipment unit (UE) and the network, and thus poor utilization of the radio spectrum, as well as additional delay, when switching from dedicated channels to common channels. In this regard, in this scenario the user equipment unit (UE) itself must obtain the temporary identifier C-RNTI by additional signaling between the user equipment unit (UE) and the network before continuing to communicate with the network. Further, the lack of information regarding which radio resources to use means that the user equipment unit (UE) needs both to detect and to read information about the radio resources on the broadcast channel in the cell before accessing the cell, and thus again incurring some additional delay when switching from dedicated channels to common channels.
What is needed, therefore, and an object of the present invention, is a technique whereby the network assigns radio resources to be utilized upon switching a connection, for a user equipment unit (UE) in a cell controlled by a drift RNC (DRNC), from dedicated channels to common channels.
A serving radio network controller (SRNC) of a radio access network assigns an appropriate temporary identifier (C-RNTI) and (optionally) radio resources to a connection which is switched from a dedicated channel to a common channel in a cell handled by a drift radio network controller (DRNC). In one embodiment, the appropriate temporary identifier (C-RNTI) and the radio resources are obtained by the serving radio network controller (SRNC) upon execution of a channel switching process (e.g., when it has been determined that a connection should be switched from a dedicated channel to a common channel). In another embodiment of the invention, the serving radio network controller (SRNC) can obtain the appropriate temporary identifier (C-RNTI) and the radio resources prior to an actual channel switch operation. In both embodiments, the obtaining of the temporary identifier and/or radio resources can be part of (e.g., an extension to) a Common Transport Channel Resources Initialization procedure.
In a first mode of the invention, the serving RNC (SRNC) assigns: (1) the cell (controlled by the drift RNC (DRNC)) to be utilized by the connection involving the user equipment unit (UE) after the channel switch operation; and (2) the C-RNTI valid in the assigned cell. In the first mode, the user equipment unit (UE) selects the specific channel resources. In the second mode of the invention, the serving RNC (SRNC) assigns (1) the cell (controlled by the drift RNC (DRNC)) to be utilized by the connection involving the user equipment unit (UE) after the channel switch operation; (2) the C-RNTI valid in the assigned cell; and (3) the specific channel resources to be utilized by the connection in the assigned cell after the channel switch operation. Both modes are more advantageous than the prior art alternative of requiring the user equipment unit (UE) to perform a additional signaling towards the SRNC to acquire a valid C-RNTI in the cell it selects.